In the disclosure of the present invention reference is mostly made to the treatment of diabetes by injection or infusion of insulin, however, this is only an exemplary use of the present invention.
Portable drug delivery devices for delivering a drug to a patient are well known and generally comprise a reservoir adapted to contain a liquid drug and having an outlet in fluid communication with a hollow infusion needle, as well as expelling means for expelling a drug out of the reservoir and through the skin of the subject via the hollow needle. The delivery device may be adapted for discrete use, i.e. injection of an amount of a drug a given number of times during the day, or they may be adapted for continuous or quasi-continuous delivery of drug through a permanent fluid connection between the delivery device and the patient. The former type of device is often referred to as a pen device and the latter type is often termed an infusion pump. A “pen” is typically a mechanical pen-formed device, however, it may have any desirable configuration just as it may comprise a motor for assisted injection of drug.
Basically, infusion pumps can be divided into two classes. The first class comprises durable infusion pumps which are relatively expensive pumps intended for 3-4 years use, for which reason the initial cost for such a pump often is a barrier to this type of therapy. Although more complex than traditional syringes and pens, the pump offer the advantages of continuous infusion of insulin, precision in dosing and optionally programmable delivery profiles and user actuated bolus infusions in connections with meals. Examples of this type of pump are shown in U.S. Pat. Nos. 4,562,751 and 4,685,903 hereby incorporated by reference. In order to provide a safe, user friendly and robust pump, most pumps are provided with a vent mechanism allowing the pump to accommodate pressure variations (e.g. due to moving interior parts, out-gassing from batteries or variation in ambient pressure), the vent being adapted to provide a certain degree of protection against the entry of water, see e.g. US 2004/0092873 disclosing an external infusion device comprising a housing having a vent port that permits the passage of air into and out of the housing and inhibits the passage of liquids into the housing through the vent port.
Addressing the above problem, several attempts have been made to provide a second class of drug infusion devices that are low in cost and convenient to use. Some of these devices are intended to be partially or entirely disposable and may provide many of the advantages associated with an infusion pump without the attendant cost and inconveniencies, e.g. the pump may be prefilled thus avoiding the need for filling or refilling a drug reservoir. Examples of this type of infusion devices are known from U.S. Pat. Nos. 4,340,048 and 4,552,561 (based on osmotic pumps), U.S. Pat. No. 5,858,001 (based on a piston pump), U.S. Pat. No. 6,280,148 (based on a membrane pump), U.S. Pat. No. 5,957,895 (based on a flow restrictor pump (also know as a bleeding hole pump)), U.S. Pat. No. 5,527,288 (based on a gas generating pump), or U.S. Pat. No. 5,814,020 (based on a swellable gel) which all in the last decades have been proposed for use in inexpensive, primarily disposable drug infusion devices, the cited documents being incorporated by reference.
The disposable pumps generally comprises a skin-contacting mounting surface adapted for application to the skin of a subject by adhesive means, and with the infusion needle arranged such that in a situation of use it projects from the mounting surface to thereby penetrate the skin of the subject, whereby the place where the needle penetrates the skin is covered while the appliance is in use.
When a fluid drug is supplied to a user, it is important that the user can visually inspect the drug to make sure that the drug is not crystallised or polymerised due to e.g. self association or penetration, or that any other visually detectable change of the drug has occurred, such as oxidation of the active drug. For insulin such visual changes are often referred to as “fibrillation”. Even weak degrees of fibrillation can be critical for a patient, as it can potentially cause allergy to insulin and change the time-profile for the insulin.
Having regard to the above-identified prior art devices, it is an object of the present invention to provide a reservoir unit with means aiding a user to check the condition of the drug, e.g. to check insulin for fibrillation, in a safe and reliable way.